Middle to late Paleozoic high-angle (45°) oblique convergence between Laurentia and composite Avalon terranes resulted in crustal shortening of ∼5:1 across the Central Maine and Bronson Hill zones of the southern New England Appalachians (USA). The Palmer zone of transpression illustrates the midcrustal expression of magmatism, metamorphism, and ductile deformation that developed in response to oblique convergence in the apparent absence of subduction. Secondary ion mass spectrometry zircon U-Pb and monazite Th-Pb ages, supplemented by zircon laser-ablation–inductively coupled plasma–single-collector mass spectrometry U-Pb ages, expand the geochronology constraining the evolution of the Palmer zone of transpression system and potential models for transcurrent collisional tectonics. Ordovician, Silurian, and Early Devonian plutons, and regional high-grade metapelitic country rocks that comprise the pre-transpressional crustal infrastructure are the same age as lithologic equivalents to the north and northeast along the orogen that did not experience high-angle oblique convergence. All plutons within the Palmer zone of transpression and adjoining areas were deformed (flattened, boudinaged, attenuated, folded, and/or ductilely sheared) by the regional transpression system. The most widespread magmatic event in the study area, which is not observed elsewhere in the Northern Appalachians, is intrusion of a diorite-tonalite suite at 370–360 Ma, the oldest rocks of which contain granulite-facies mineral assemblages and all of which are deformed. Leucopegmatites that intrude pelitic paragneisses, which likely formed in response to high-grade metamorphism and which are all deformed, are 370–355 Ma in age. All metapelitic paragneisses contain foliations and lineations that are synkinematic with retrograde garnet + K-feldspar → sillimanite + biotite assemblages and fabrics that formed during vertical and lateral crustal escape in response to extreme shortening. Contemporaneous diorite-tonalite magmatism and regional high-grade metamorphism are interpreted to reflect regional-scale heating of the crust preceding inception of the transpressional system. Transpressional deformation of both plutons and paragneisses indicates shortening commenced after crustal thermal conditions peaked (ca. 355 Ma). Monazite in paragneiss, the formation of which in most samples is linked texturally to formation of transpressional fabrics, yielded a continuum of Th-Pb ages of ca. 360–330 Ma, indicating transpression continued after peak thermal conditions. The extreme crustal shortening of the Bronson Hill and Central Maine zones from Maine to southern New England, pre-transpressional magmatism, and high-grade metamorphism overprint an Acadian (ca. 400–370 Ma) magmatic-metamorphic infrastructure that occurred in the absence of subduction. The transpressional system exhibits all predicted thermal, magmatic, deformation, metamorphic, and exhumation/erosion characteristics of mantle lithospheric foundering (delamination, detachment, or drip) in response to extreme lithospheric shortening and vertical stretching at ca. 375–370 Ma, leading to advection of heat to the lower continental crust and attendant magmatic and metamorphic responses over the time span 370–355 Ma.

中文翻译：

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美国新英格兰中南部帕尔默高压区的锆石和独居石年代学：在北阿巴拉契亚造山带晚古生代斜碰撞中，变形时间，高级变质作用和岩石圈形成的时间受到限制

劳伦西亚和复合阿瓦隆地体之间的中古生代高角度（45°）倾斜交汇，使整个新英格兰阿巴拉契亚山脉（美国）的缅因州中部和布朗森山地带的地壳缩短了约5：1。帕尔默地压带解释了岩浆作用，变质作用和延性变形的中壳表达，这些作用是在显然没有俯冲的情况下响应斜向会聚而形成的。二次离子质谱法锆石U-Pb和独居石Th-Pb年龄，再辅以锆石激光烧蚀-电感耦合等离子体-单收集器质谱法U-Pb年龄，扩大了地质年代学，限制了转导系统帕尔默带的演化，跨流碰撞构造的潜在模型。奥陶纪，志留纪和早泥盆纪的云母，构成压前前地壳基础结构的区域性高级成岩成岩乡村岩石的年龄与造山带北部和东北部未经历高角度倾斜会聚的岩性等效年龄相同。受区域压迫系统的影响，帕尔默压榨带及其毗连区域内的所有云母都发生了变形（变平，弯曲，衰减，折叠和/或韧性剪切）。在研究区中最广泛的岩浆事件是在370-360 Ma的闪长岩-绿柱石岩组侵入，该岩岩层中最古老的岩石含有花岗石相矿物组合，并且所有这些岩浆活动都是在阿巴拉契亚北部的其他地方没有观察到的。变形了。侵入高岭变质岩的白云母岩，可能是由于高级变质作用而形成的，并且全部变形了，年龄在370–355 Ma之间。所有变质性的石格纹都含有与逆向石榴石+钾长石→硅线石+黑云母组合和在垂直和横向地壳逃逸期间形成的织物动力学响应的叶和纹。解释了同时闪长岩-黄铁矿的岩浆作用和区域高级变质作用，以反映在建立超压系统之前地壳的区域尺度加热。Plutons和Paragneisses的超压变形都表明地壳热条件达到峰值（约355 Ma）后开始缩短。帕纳涅斯石中的独居石，其在大多数样品中的形成与构造上与压迫织物的形成有关，产生了连续的Th-Pb年龄约25年代。360–330马，表明在高温条件下继续压抑。从缅因州到新英格兰南部，布朗森山和缅因州中部地区的极端地壳缩短，压前岩浆作用和高级变质作用覆盖了阿卡迪亚（约400-370 Ma）的岩浆变质基础设施，该基础设施是在没有俯冲。响应于岩石圈的极端缩短和垂直拉伸，该压变系统表现出了所有预测的地幔岩石圈沉陷的热，岩浆，变形，变质和发掘/侵蚀特征（分层，分离或滴落）。375-370 Ma，导致在370-355 Ma的时间段内热量向对大陆下地壳平流，并伴随岩浆和变质作用。从缅因州到新英格兰南部，布朗森山和缅因州中部地区的极端地壳缩短，压前岩浆作用和高级变质作用覆盖了阿卡迪亚（约400-370 Ma）的岩浆变质基础设施，该基础设施是在没有俯冲。响应于岩石圈的极端缩短和垂直拉伸，该压变系统表现出了所有预测的地幔岩石圈沉陷的热，岩浆，变形，变质和发掘/侵蚀特征（分层，分离或滴落）。375-370 Ma，导致在370-355 Ma的时间段内热量向对大陆下地壳平流，并伴随岩浆和变质作用。从缅因州到新英格兰南部，布朗森山和缅因州中部地区的极端地壳缩短，压前岩浆作用和高级变质作用覆盖了阿卡迪亚（约400-370 Ma）的岩浆变质基础设施，该基础设施是在没有俯冲。响应于岩石圈的极端缩短和垂直拉伸，该压变系统表现出了所有预测的地幔岩石圈沉陷的热，岩浆，变形，变质和发掘/侵蚀特征（分层，分离或滴落）。375-370 Ma，导致在370-355 Ma的时间段内热量向对大陆下地壳平流，并伴随岩浆和变质作用。400-370 Ma）在没有俯冲的情况下发生的岩浆变质基础设施。响应于岩石圈的极端缩短和垂直拉伸，该压变系统表现出了所有预测的地幔岩石圈沉陷的热，岩浆，变形，变质和发掘/侵蚀特征（分层，分离或滴落）。375-370 Ma，导致在370-355 Ma的时间段内热量向对大陆下地壳平流，并伴随岩浆和变质作用。400-370 Ma）在没有俯冲的情况下发生的岩浆变质基础设施。响应于岩石圈的极端缩短和垂直拉伸，该压变系统表现出了所有预测的地幔岩石圈沉陷的热，岩浆，变形，变质和发掘/侵蚀特征（分层，分离或滴落）。375-370 Ma，导致在370-355 Ma的时间段内热量向对大陆下地壳平流，并伴随岩浆和变质作用。或岩石滴落），以应对极端的岩石圈缩短和垂直拉伸（大约200摄氏度）。375-370 Ma，导致在370-355 Ma的时间段内热量向对大陆下地壳平流，并伴随岩浆和变质作用。或岩石滴落），以应对极端的岩石圈缩短和垂直拉伸（大约200摄氏度）。375-370 Ma，导致在370-355 Ma的时间段内热量向对大陆下地壳平流，并伴随岩浆和变质作用。